The long-term research goal of this project is to elucidate common mechanisms by which defects in microtubule-(MT)-based transport promote neurodegenerative disease. Though neurodegenerative diseases are often divergent in symptoms and etiologies, defective long-range transport along MT tracks and the biological dysfunction of the RNA metabolism protein TDP-43 are emerging as common factors associated with a broad range of disorders, including Amyotrophic Lateral Sclerosis (ALS), Alzheimer's disease, and Parkinson's disease. The roles of both TDP-43 and transport defects in driving pathogenesis are poorly understood. The goal of the work proposed here is to investigate the relationship between TDP-43 and long- range transport and determine if they act synergistically to promote disease. Simple and genetically tractable yeast models of TDP-43-based pathology have been valuable, but yeast do not use MTs for long-range cellular transport as humans do and thus are less well suited to dissect is relationship with TDP-43. To understand this relationship, the filamentous fungus A. nidulans will be developed as a model system for studying both TDP- 43-based toxicity and MT-based transport. A. nidulans has genetic tractability comparable to that of yeast, but unlike yeast, uses MTs for long-range transport in cellular regions that closely resemble mammalian neurons. Second, this model will be used to test two alternative hypotheses about the relationship between transport and TDP-43. The first hypothesis is that pathogenic species of TDP-43 broadly impair MT-based transport processes. To test this, MT-based cargos in A. nidulans will be fluorescently-tagged and tracked during TDP- 43 expression in order to detect defects. The second hypothesis is that defects in MT-based transport promote pathogenic features of TDP-43 pathology, such as increased localization to the cytoplasm. This hypothesis will be tested by generating known pathogenic mutations in the MT-based transport machinery and subsequently investigating the biological behavior of TDP-43. Finally, to identify novel factors related to either TDP-43 biology or MT-based transport that contribute to disease, an unbiased and systematic mutagenesis screen will be performed in the A. nidulans pathology model. This work will not only illuminate the causes of TDP-43 based pathology, but also provide a paradigm for elucidating and understanding the pervasive transport defects of neurodegenerative diseases.